The present invention is directed to retractable cord reels, and in particular to a seamless, spliceless conductive cable having a flat portion and a round portion for use in a retractable reel.
Retractable cord reels have been used in various applications to retractably store various types of cables. The cable held on the reel typically has a stationary end portion and a portion that may be extended from and retracted back into the reel. Conventionally, the reel comprises a spring-loaded spool on which the extendable portion of cable is wound. The extendable portion of the cable may be withdrawn from the reel, causing the spool to rotate against the force of the spring. Upon release of the cable, the spring causes the spool to rotate in the opposite direction thereby retracting the cable back onto the spool. A problem common to all prior art cord reels is providing a continuous electrical connection between the rotating extendable portion of the cable and the stationary end portion. Two basic types of cord reels have been developed to address this problem.
One type of reel utilizes rotating contacts, commonly placed between the rotating reel and a stationary housing. The stationary end portion of the cable is separate from the extendable portion. The stationary cable is connected to the contacts carried by the housing, and the extendable portion is connected to the contacts carried by the reel. When the reel rotates, substantially continuous contact is made between the rotating contacts. However there are numerous, well documented disadvantages of cord reels having moving contacts. Moving contacts have a propensity to spark, making such reels unsuitable for use in wet environments, hazardous environments and in medical applications, among others.
To overcome these problems, a second type of retractable cord reel has been developed that eliminates contacts. The reel comprises a spool on which the extendable portion of cord is held, an expansion chamber in which a fixed length of cable is spirally wound. The two cable portions are connected, typically in or adjacent the hub of the spool. As the spool rotates the spirally wound, fixed cable expands and contracts within the expansion chamber. An example of reels of this type is disclosed in U.S. Pat. No. 5,094,396 to Burke, the disclosures of which are hereby incorporated by reference.
It has been well known in the art that reels of the second type function properly and enjoy an acceptable service life when the fixed cable portion in the expansion chamber is flat, and the extendable cable portion is round. If the extendable cable portion is flat, it will not retract properly on the spool. If the fixed cable portion is round, it tends to twist and snarl in the expansion chamber. Accordingly, a combination flat and round cable is required. Conventionally, flat-round cables, i.e., a cable having a flat portion and a round portion, have been fabricated by splicing a flat cable to a round cable. This is acceptable in many, but not all applications. In hazardous and wet environments, spliced cables are unacceptable. Further, some electronic applications, splices in cable conductors can cause distortions to electronic signals carried by the cable.
U.S. Pat. No. 4,384,688 to Smith discloses a reel assembly having a reel about which a telephone cable is retractably wound. A helically coiled spring urges the reel to retract the telephone cable into the reel assembly. The telephone cable is seamless and has a constant cross-sectional shape at all points along the cable. Although it avoids the use of a spliced cable, the Smith reel is not optimal since it does not utilize a flat-round cable as described above.
Although numerous designs for retractable cord reels have been proposed, there has been no adequate solution for a retractable cord reel having seamless cable that can be used in hazardous and wet environments that is durable and has a long service life. There is and has been significant demand for such a reel for many years.
The invention is directed to a seamless flat-round conductive cable for use in a retractable cord reel of the type having a rotating spool and a cable expansion chamber. The flat-round conductive cable comprises a first cable portion adapted to be held or disposed in the expansion chamber of the reel. The first cable portion comprises a plurality of elongated, seamless conductive members, each conductive member having a conductor substantially covered by an insulating layer. A second cable portion is adapted to be retractably held on the spool of the reel. The second cable portion likewise comprises a plurality of elongated, seamless conductive members, each having a conductor substantially covered by an insulating layer. The conductive members of the second cable portion are seamlessly continuous, i.e., unitary, with respective ones of the conductive members of said first cable portion. One or more of any of several means are employed to maintain the first cable portion in a substantially flat configuration and said second cable portion in a substantially round configuration.
The first or flat portion of the cable preferably comprises plural conductive members arranged in a substantially parallel, side-by-side configuration. The first portion of the cable is held in this configuration in any one of several different ways. One means for maintaining the first cable portion in said substantially flat configuration is bonding the conductors together, side-by-side. Chemical bonding with ultraviolet curing has been found to work well. If the insulating layer on the conductors is a thermoplastic or resin, such as polyvinyl chloride, heat or thermo-bonding may used.
A preferred means for maintaining the first cable portion in a substantially flat configuration is a jacket. The jacket may be woven nylon, which will function to protect the conductive members from abrasion, reduce friction in the expansion chamber and provide smoother operation, as well as holding the conductors in a flat configuration. Alternatively, the jacket may be comprised of a conductive material such as copper. A conductive jacket will provide the additional benefits of functioning as an EMF shield or may be used as an additional conductor, such as a ground. If the jacket acts as a ground conductor, one less conductive member is required, thus beneficially reducing the size and cost of the cable. A conductive jacket may be woven or spirally formed.
Another preferred means for maintaining said first cable portion in a substantially flat configuration comprises strands woven between the conductive members of the first cable portion. The strand is woven between conductive members to bind them together in a parallel, side-by-side configuration, thereby forming a substantially flat cable. Weaving is relative inexpensive, does not appreciably add thickness or weight to the cable, and allows the conductive members a small amount of relative movement between them, which provides significant benefits in a smaller, more durable retractable cord reel.
The second, round portion of the cable may likewise be formed several different ways. A substantially round configuration is achieved by twisting the plural conductors together. The twisted configuration may be maintained without additional holding means. Nevertheless, one may bond the conductive members together as described above. Preferably, a jacket is added over the conductive members. The jacket may desirably comprise an elastomeric material to protect the conductive members from abrasion and moisture. Alternatively, the jacket may comprise a fabric braid, such as nylon. As described above, a conductive jacket may be employed as an EMF shield or as an additional conductor. It is particularly desirable to use a conductive jacket as a conductor, such as a ground conductor, and thereby eliminate one of the standard conductive members. This will substantially reduce the diameter of the round or second portion of the cable. A greater length of retractable cable may thereby be provided on spool of a given size. If a conductive jacket is used, it may be desirable to apply an insulating cover over the conductive jacket of the second portion of the cable.
If a jacket is used to maintain the two cable portions in the respective flat and round configurations, the jacket may desirably be continuously woven over both portions of the cable.
Several means for holding the cable in a flat/round configuration have been disclosed. It is to be understood that the invention as broadly claimed is not limited to these specific means but should be construed to cover all means that will provide the desired result of maintaining a flat/round cable configuration.
The conductive members comprise a conductor and layer of insulating material substantially covering the conductor. The conductor preferably comprises a multiplicity of wire strands. Stranded wire is has better resistance to fatigue than solid wire. The first or flat cable portion is subjected to considerable fatigue in the cable expansion chamber, as described below. Likewise, the round or retractable cable is subjected to a variety of forces including fatigue. A greater number of strands will beneficially provide a more durable and longer life to the retractable cord reel.
The cable may also have a third cable portion with a substantially round configuration, with the flat cable portion being disposed between the two round cable portions. The third cable portion has a plurality of seamless conductive members, each being seamlessly connected to the respective conductive members of the first cable portion.
Accordingly, the invention presents a facile solution to the long-standing problems encountered in the retractable cord reel art. The potential risk of a spark in a cord reel having the cable of the invention is greatly reduced, because the cable is continuous and seamless, and splices and contacts have been eliminated. Accordingly, a cord reel having the flat-round cable of the invention may be advantageously used in environments that heretofore have been unsuitable for retractable cord reels. Potential new uses include hazardous environments (e.g., chemical, petroleum, dust laden), wet environments (e.g., outdoors, marine), medical environments such a hospitals, and industrial environments. Specific retractable cord reel applications that were not heretofore possible include all-weather power cord reels for wet/dry vacuums, electric vehicle charging, engine heater connections, and electric hook-ups for boats.
Another application of the invention is to sensitive electronic applications such as microphone cables. Since the cable of the invention is seamless, electronic distortions caused by splices are eliminated.
Additional commercial applications, features and advantages of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiments, which is made with reference to the drawings, a brief description of which is provided below.